1. Field of the Invention
The present invention is related to a process for constructing a green tire and to an expandable drum on which a green tire is formed.
2. Discussion of Background Information
Generally, bead cores, e.g., Pierce cores for motor vehicles and hexagonal cores for trucks, are produced by devices that are separate from the device for forming a green tire (tire blank). As is known, the filler (or bead fitting profile) is mounted on each bead core on this device.
A carcass is assembled while lying flat on a device having a radially expandable drum with a substantially horizontal axis of rotation and with a thick-walled casing made of rubber or similar material that forms a periphery of the drum that is adequate to balance the compression. As is customary, the carcass assembly is started by applying the sidewalls and/or the substantially air-tight inner liners. Then one or more bead-enforcing profiles, also known as "chafers", are mounted in the usual manner. These chafers can be reinforced with textile or metallic stress supports, which, when used in truck tires, are subjected to a high degree of stress. Then a first and, if necessary, a second carcass ply is applied which generally contains textile and/or metallic stress supports in an axial arrangement.
The bead cores are then slid or guided over the drum and axially positioned. Thereafter, the bead cores and the flat carcass are radially pressed against each other via expansion of the drum. This compression assists the bonding or joining of the inner surfaces of the bead cores to the external surfaces of the carcass.
Then the diameter of the drum is compressed and the carcass with the set bead cores is pulled off the drum, and the cores are conveyed to a preshaping device.
On the preshaping device, the edges of the carcass, i.e., the areas located axially outside the set bead cores, are turned up so that the axially external surface of the respective bead core bond with an axially external surface of the filler, and possibly with the axially external surface of the carcass. If fillers are utilized, they must be installed no later than immediately prior to turning up the carcass. However, as mentioned previously, the fillers are generally applied to the beads immediately after the bead has been produced. Accordingly, preshaping occurs either after or during the turning up of the ends of the carcass ply. The side strips, which are preferably applied at the start of assembly, are knocked upward, after preshaping, by bellows located axially outside of each core.
In many tires, a shoulder cushion profile is arranged between a bottom belt ply and a carcass ply. The existence, shape, and arrangement of these shoulder profiles, as well as whether they are to be mounted to the carcass in a flat or preshaped position do not influence the utility of the present invention.
After turn-up and preshaping, the green tire is completed in a known process, e.g., with belt plies or, if necessary, a band, with sidewalls, and, if necessary, with multilayer tread rubber. However, the number of belt plies, the alignment and mounting of their stress supports, the type of tire, the type and construction of the tread, the sequence of mounting the tread layers and sidewalls, i.e., the manner of completing the tire is not the focus of the present invention.
The sliding of the bead cores over the drum, the axial positioning of the bead cores, and the subsequent radial compression of the bead cores and the carcasses are known as "beading." The present invention is related to the beading process and to the type of compression necessary between prefabricated core and carcasses to achieve the bonding.
A known technique for manufacturing a bond that is free of air bubbles between the carcass and bead cores consists of, rather than manufacturing the cores on a separate device, making the bond directly on the drum via coiling after applying the carcass plies to be mounted to the core setting. However, this process has several disadvantages. In particular, only such cross-sectional forms of bead cores are possible that have an inside running parallel to the drum surface are possible, i.e., no hexagonal core can be utilized unless special measures are taken, and the output of the very costly drum used to construct the green tire, including its peripheral units, such as a servicing unit, a drive unit, a rolling unit, etc., is reduced during the core construction. Thus, utilizing a separate core construction device is much more cost-effective because it requires less space than maintaining additional building drums for green tires to achieve an equal green tire output per production time. Moreover, while it is advantageous to coil the cores immediately after the rubber extrusion of the core wires via the extruder supplying the core wires because the rubber still flows particularly easily and the surface is not threatened by the entry of dust, little space is available for one or more extruders due to the numerous necessary conveyors for a tire building drum.
Another generally utilized technique for core placement includes manufacturing the bead cores, preferably with the filler, with a separate device, and producing the carcass laying flat on a radially expandable drum having a thick walled casing made of rubber or similar material that forms the periphery of the drum and that adequately balances the compression. Thus, the carcass is produced having a diameter smaller than a maximum diameter for the drum.
This smaller drum diameter is selected so that an outside diameter of the carcass is somewhat smaller than an inside diameter of the bead cores to be placed. The ordinarily skilled artisan is familiar with dimensioning a required minimum play between the outside of the carcass and the inside of the core bead to prevent premature contact between the two.
The bead cores may then be slid or guided over the drum and axially positioned. Then, the drum, at least in the axial area in which the bead cores are positioned, is expanded to a diameter so that the outside diameter of the carcass is greater than the inside diameter of the bead cores. Due to this dimensional difference, the bead cores and the carcass are radially pressed against each other. Thus, the compression of these components produces an adequate bonding or joining between the inner surface of the core beads and the outer surface of the carcass, which still lays flat.
The drum may then be compressed to a smaller diameter so that the carcass and set bead cores may be removed from the drum. The carcass may then be forwarded for further processing in a preshaping device. In the preshaping device, the carcass may be centrally wedged underneath the bead cores via expandable rings that are axially movable. A bellow, which may be located in an axial center of the preshaping device and collapsed during conveyance of the carcass to the drum and during the conveyance of the green tire away from the drum, may be inflated to touch the inner wall of the carcass and lift the inner wall between the bead cores.
Then the boundary areas, which are located axially outside the placed bead cores, may be turned up, and the carcass may be preshaped and completed further, e.g., with belt plies and treads, into a green tire.
Tire manufacturers are pressured by their customers, in particular, the original equipment manufacturers, to improve the concentricity, an aspect of tire uniformity, of the tire. In the past, this goal was achieved via measures taken after tire vulcanization. The most well known of these measures being grinding the tread pattern at points that show excessive radial force.